As the advantages of fiber optic based communication and control of industrial processes becomes better known, increasing emphasis is being placed on various methods of simple, inexpensive, and reliable communication of optically sensed physical parameters, or measurands. Optical analysis of certain fluid materials offers known improvements over other techniques.
The measurement of the light transmitting or light scattering properties of a fluid ordinarily requires that a beam of light or radiant energy be passed through the fluid and subsequently directed towards a radiant energy detector. Optical apparatus for accomplishing this task have been used in which discrete components such as lenses, mirrors, or internally reflecting light guides are employed for the sampling apparatus. Optical fibers may be used to convey the light to the sensing apparatus and back to detection equipment. Examples of such techniques are illustrated in U.S. Pat. Nos. 4,591,268 to Lew ('268); 4,320,978 to Sato ('978); and 4,152,070 to Kushner et al ('070). These methods are generally unsuited for direct submersion within the test fluid because the optical surfaces are derogated by fluid contact, i.e., dirt erosion, pitting, and dissolving of the surfaces.
The use of fiber optic light guides is recognized for permitting the measurement of the light transmitting or scattering properties of fluids in harsh environments, such as a process container or pipeline containing the fluid of interest. Thus, U.S. Pat. Nos. 4,040,743 to Villaume et al ('743) and 4,561,779 to Nagamune et al ('779) depict apparatus for the in-situ measurement of fluid suspensions. A similar approach described by H. Raab in Technisches Messen, 50, 1983(12), p. 475, is employed for the in-situ assay of certain fluids. A common feature of these known methods is the use of relatively small prisms having planar surfaces which act to bend a light beam through 90 degrees. Such prisms can be expensive to fabricate and difficult to align.
Conical reflecting elements have been previously described in the literature (cf. M. Rioux, et al, Applied Optics, 17(10), 1978, p. 1532). Their use has been primarily as imaging devices for objects disposed along the conical reflecting element's axis of revolution. As will become evident from the subsequent disclosure, the method and apparatus of the invention described herein depart from these known configurations and permit utilization of the interior conical reflecting surface in an off-axis manner.
In addition, since the present invention has application in the fermentation arts, it is useful and often necessary to minimize bubbles in the measurement area. Known passive bubble reducing techniques are inadequate when applied to a fermentor environment. Typically intricate and narrow passageways designed to promote drainage of foamy samples are ineffective, and may be prone to blockage from the solution, which is typically cell-laden.
For this reason, the present invention comprehends the inclusion of a valved still well or stilling chamber from which the bubbles and foam are effectively drained prior to measurement. The combination probe thus incorporates a stilling well chamber, which may be either electrically or pneumatically valved, and a novel optical probe. Such a valved still well embodiment includes an `open` position in which the solution is free to pass through the measurement chamber, and a `closed` position in which the bubbles and/or foam in the solution are permitted to drain briefly before the measurement.
For the purposes of this limited description, "fiber optic" "optical fiber", "light guide", and "radiant energy pathway" refer to optical communication paths, generally optical fibers. As used herein, the terms "radiant energy" and "light" are used interchangeably to refer to electromagnetic radiation of wavelengths between 3.times.10.sup.-7 and 10.sup.-9 meters, and specifically includes infrared, visible, and ultraviolet light. For simplicity, such electromagnetic radiation may be referred to as simply "light." These terms specifically include both coherent and non-coherent optical power. "Monochromatic" refers to radiant energy composed substantially of a single wavelength. "Collimated" light refers to radiant power having rays which are rendered substantially parallel to a certain line or direction.